1. Field of the Invention
This invention relates to high pressure hydraulic systems and more particularly to apparatus and a method for suppressing the noise associated with pressure surges in high pressure hydraulic systems, such as those in injection molding machines.
2. Description of the Prior Art
In high pressure hydraulic systems, when the hydraulic pressure is released so that high pressure hydraulic fluid can escape to a lower pressure portion of the system, a rapid release of the high pressure frequently results in a surge that causes a cracking-type noise that can have an objectionably high intensity. Although the noise can be reduced by very gradually releasing the high pressure, such a gradual release would undesirably result in significantly longer times for operating cycles for equipment embodying such high pressure systems. Because it is generally desired that hydraulically operated production equipment be operated as rapidly as possible, to permit high volume production of articles such as, for example, molded parts made by an injection molding machine having a hydraulic clamp system, a rapid release of high hydraulic pressure is preferred to provide shorter operating cycle times. However, rapid releases of pressure should be accompanied by a reduction in the sound intensity caused by the pressure reduction, in order to provide an improved work place environment.
Although in the past the use in hydraulic circuits of pilot-operated check valves and counterbalance valves has been suggested in order to reduce the intensity of pressure surges that occur upon release of high pressures, even the use of such valves, which provide slight delays to permit more gradual decompression of the system, still involves undesirable noise when operated at reasonably rapid cycle times that are desired for high volume production.
It is therefore an object of the present invention to provide an hydraulic circuit that permits rapid release and decompression of a high pressure hydraulic fluid, without creating excessive environmental noise.
It is another object of the present invention to provide an improved hydraulic system in which noise can be reduced without the addition of numerous complex and expensive additional valves or additional hydraulic circuitry, which can increase the initial cost of such a system, as well as the operating costs arising from the likelihood of higher maintenance requirements.